The anonymous officials say Russia has set up an air traffic control tower and transported prefabricated housing units for up to 1,000 personnel to an airfield serving the Syrian port city of Latakia.

Russia has also requested the rights to fly over neighbouring countries with military cargo aircraft during September, according to the reports.

The claims, which will raise fears that Russia is planning to expand its role in the country’s civil war, will ratchet up tensions between Moscow and Washington over the future of Syria and its brutal ruler.

Mr Obama on Friday met King Salman of Saudi Arabia to repeat their demand that any lasting settlement in Syria would require an end to the Assad regime.

It leaves the US and Russia implacably opposed in their visions for Syria.

Russian troops are said to be 'fighting alongside Assad's army against Syrian rebels' Photo: @ValkryV

Last week the Israeli daily Yedioth Ahronoth cited Western diplomatic sources saying that Russia was on the verge of deploying “thousands” of troops to Syria to establish an airbase from which the Russian air force would fly combat sorties against Isil.

Those details appear to be backed by satellite images of a Russian base under construction near Latakia